Phase modulation system and apparatus



April 14, 1953 D. B. HARRIS PHASE MODULATION SYSTEM AND APPARATUS 6 Sheets-Sheet l Filed Jan. 20, 1950 April 14, 1953 D. B. HARRIS 2,635,226

PHASE MODULATION SYSTEM AND APPARATUS Filed Jan. 20, 1950 6 Sheets-Sheet 2 /7 7\ I Z/ /fg /f SP1/[5P OSC/LLTg/f L 7? fem?? sal/ECE j Z of .svg/wus l fa/ Ir 5:1. z.

INVENTOR.

APT 14, 1953 D. B. HARRIS 2,635,226

PHASE MODULATION SYSTEM AND APPARATUS Filed Jan. 20 1950 6 Sheets-Sheet 5 INVENTOR. @0A/,420 f3 #HPF/5 April 14, 1953 D. B. HARRIS 2,635,226

PHASE MoDULATIoN SYSTEM AND APPARATUS Fil'ed Jan. 2o, 195o s sheets-Sheet 4 IN VEN TOR. 00A/, 10 5. HARP/s April 14, 1953 D. B. HARRIS PHASE MoDULATIoN SYSTEM AND APPARATUS Filed Jan, 2o, 195o 6 Sheets-Sheet 5 Iri 7.

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INVENTOR. @0A/,Q0 MPP/.S

April 14, 1953 Filed Jan. 20, 1950 fem )7 fev,

D. B. HARRIS PHASE MODULATION SYSTEM AND APPARATUS 6 Sheets-Sheet 6 Patented pr. i4, 1953 UNITED PHASE MODULATION SYSTEM AND APPARATUS Donald B. Harris, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a

corporation of Iowa Application January 20, 1950, Serial No. 139,711

12 Claims.

This invention relates to electric signalling systems, and more especially to such systems as employ phase-modulated carriers.

A principal object of the invention is to provide an improved phase modulation signalling system.

Another object is to provide a system of phasemodulated carrier, wherein very wide and signalcontrolled phase deviation in the carrier can be procured.

Another object is to provide a system for converting input signal voltages into a phasemodulated carrier, by employing conventional amplitude modulation techniques.

Another object of the invention is to provide novel forms of phase converters.

A feature of the invention relates to a phasemodulated carrier system for producing a very wide signal-controlled phase deviation in the carrier, while maintaining a linear relation between the signal input amplitude and the carrier phase deviation.

Another feature relates to a phase-modulated carrier system, wherein original input signals are converted into two equal-frequency signals of quadrature phase relation, which signals are then used to amplitude modulate, in separate channels, two equal-frequency carriers also of quadrature phase relation and with the amplitude-modulated carriers added, to produce a phase-modulated carrier.

Another feature relates to a phase modulation system employing a sweep oscillator which simultaneously feeds a sine phase converter and a cosine phase converter, to which converters the input signals are also applied to produce, in separate channels, sine and cosine modulating functions correlated with the input signals; and a source of carrier frequency is provided for developing two quadrature phase components which are respectively amplitude-modulated by said sine and cosine functions, and with the amplitude-modulated outputs combined to produce a phase-modulated carrier.

A further feature relates to the novel organization, arrangement and relative interconnection of parts which cooperate to provide an improved phase modulation system.

Other features and advantages not particularly enumerated, will be apparent after a consideration of the folowing detailed descriptions and the appended claims.

Referring to the drawing,

Fig. l is a schematic showing, in block diagram form, of a phase modulation system according to the invention.

Fig. 2 is a schematic diagram of a phase converter according to the invention.

Fig. 3 is a sectional view of the tube of Fig. 2, taken alongthe line 3-3 thereof.

Fig. 4 is a graph explanatory of the operation .0f the tube of Fig. 2.

Fig. 5 is a schematic illustration of a modified form of phase converter.

Figs. 6, 'l and 8 are graphs explanatory of the converter of Fig. 5. x

Figs. 9, 9A and 10 are further modifications of the phase converter of Fig. 2.

It can be shown that when two carrier fre'- quencies in quadrature relation, for example sine and cosine, are respectively modulated by separate modulating functions, the complex transmitted spectrum can be expressed as follows:

where ei is the instantaneous voltage of the complex modulated wave, Fand) is a modulating function identified as being associated with a cosine carrier by subscript a, 1L is any integer, w is the angular frequency of a fundamental carrier wave, and Fbn(t) is a modulating function identified as being associated with a sine carrier by subscript b, then, in order to demodulate the cosine carriers, it is only necessary to multiply by cos nwt, and integrate, to obtain a demodulator output current,

while, if it is desired to demodulate one of the sine carriers, the complex wave is multiplied by sin mut, and the result is integrated to obtain /w o e,-(s1n mvt)dt= The factor ya depends on the characteristics of the demodulatng device.

In accordance with one feature of the present invention, the desired modulating functions are produced by special phase converters controlled jointly and simultaneously by the audio frequency or similar input signals, and a local sweep oscillator. Thus by making the angles of the function Fand) and the function Fbn) linear With respect to an original modulating signal, and by selection of a suitable form for these two modulating functions Fand) and Fand), satisfactory phase modulation of a carrier frequency can be achieved while employing conventional amplitude modulation techniques.

Inspection of Equation 1 shows that the modulating functions Fand) and Fund) must, in order to specify fully a modulated wave, have a form of the following general nature:

Fan (t) ==7rEknGan (t) and rate of change with time must be sufficiently small to permit them to be considered constant during the period of integration, they may in general be any functions of time. For phase modulation purposes, we assign a restricted form to the modulating waves Gand) and Gb('t) in ac'- cordance with the following equations,

where Emn is the amplitudeof'the modulating wave and pn is the independent variable, the Value of which is controlled by the modulating voltage being transmitted. Then the modulating 'functions become n Fand) =yrEknEm cos p :Eon cos 'dm (8) and l n Fbt) =7TEk`nEmn Snlm--Eon -`Siffl 'tlm (9) where Een is used in place of y'TEknEmnfor the sake of 'simplicityof notation, and is the maximum amplitude of the modulated envelope. For the momentwe need not concern ourselves with the 'eif'iact relation between qbn'and the modulating voltage,"but merely note that if the 'modulation processhas been carried out in accordanoe with theserelationships, so that the transmitted Wave -s of the form,

egg-2E... 'cts e.. ccs awt-Filename., sin ma] (19) then. the original phase-dependent modulating functions can be recovered at the'receiving ter.-

minal by multiplying by a wave having the same frequency and phase as the carrier, and integrating, in the manner of Equations 2 and 3, which are here written in the following form:

' identity.

cos A cos B sin A sin B`=`cos (A-B) (13) which leads'im'mediately to the equation, 'e,=`,[2E}, cos eos nwt-AI-ZEMsin sin mot] =2E,; cos (mut-km) '.(14) e equation states in effect that if a carrier wave is amplitude modulated by a modulating function to vproduce a first modulation'product, and'if the same carrier wave'in quadrature is amplitude-,modulated by thel same modulating function also in quadrature, to form a second modulationproductpthen the sumof the first andV second mo'dulation products is a phasermodulated wave. The importanceof the 'relationship Yresides 'in the fact that theact'ual modulation process in whiehtl'ienodulating function is impressed on`the' carrier 'nvolv'es'amplitude modulation only. Conventional and simple amplitude modulators may therefore be employed in the radio-frequency Vsection to produce the required phase modulation: VThe preparation of the necessary :modulating vfunctions to beappli'ed to theramplitudemodulators may be carried out at' modulating frequencies. `Q v jltaremains, of course, todeter'mine just what 'sert `of 'modulating function we need to create in order to produce, through this process, a phasemodulated vwave in which the phase 'deviation is a linear function of the fundamental modulating voltage, emu. It is immediately seen that the primary requirement is expressed by the equation,

ofthedeviee'employed to set up the modulating function.Y Since the modulating waves required Vat the output of this device are specied by Equation's'6 'and 7, we immediately have, by substitution ofP (15) in these equations, the requirement that the output of the device, which might be called a phase converter must be Gauw) :E'mn COS kemn (16) and Y Gbn(t)=Em1i Sin 1681111 (17) Under'thes'e conditions, the 'equation of the modulated wave becomes e,=2E cos-('nu't-kem r'(18) which is the equation of a phase-modulated Wave having a phase deviation proportional Eto 'the modulating voltage.

summarizing the requirements ofthis typeof phase-modulation system, it is seen Athat'the first -step is the generation, by means of phase-converters, of two modulating Vwavesythe instanta- "neous values of which areproportional respectively to the vcosiney and to the 'sine lof an'angle which in turn is proportional t'o'themodulating voltage. These two modulating l'waves are used respectively to 'amplitude-modulate a cosinecarrier and a sine carrier, and the outputscof the amplitudemodulators are added. The result is a phase-modulated Wave in 'which the phase de- Viation is proportional'to the original modulating voltage. c

Referring to Fig. 1 of the drawing, the block lil represents any well-known source of modulating voltages, such for example as 'a voice frequency or audio frequency voltage source, This signal voltage is represented as emn andis'mpressed in parallel von a cosinephase vconverter lland a sine phase converter I2. The devices lljandjl2 are supplied with a local sweep L frequency from asweeping oscillator I3 vof any wellknown type, such for vexample as Aa `Hartley, Colpitts, or tuned grid-tuned plate oscillator. This oscillator may, for example, have 'a fundamental frequency of one megacycle per second. The device Il providesat its output thejmodulating functionV Gan(t)=Emn cos Icy-em", which is identical with Equation 16 explained hereinabove; While the device l2 produces at its output the modulating function Gzm(t) :Em sin Zwem, which, it will be observed, is the same as Equation 17 explained hereinabove.

The modulating function Gand) is'applled to a balanced amplitude modulator I3a, and the modulating function GMU) is applied to a simi lar. balanced amplitude modulator I4. The modulators l3a and I4 are also fed in the yusual balanced relation from alooal carrier source l5 having Vappropriate phasing networks to produce tow equal-frequency 'carrier outputs, but with the outputs in quadrature phase relation. "For a detailed disclosure of 'a balanced amplitude modulator, reference mayv be had tothe Radio Engineers Handbook by'F. E. YTerman, first edition, second impression, page 551, Figure'22, and likewise for 'a detailed disclosure of vthe carrier source and phasing networks represented by block I5, reference may be had to the same volume, page 480, Figure 1(a), and page 949, Figure 56(a), respectively. The carrier` output Ekn cos (met) is fed to modulator I3a, while the carrier Ekn sin (mut) is applied to the balanced modulator I5. There is produced at the output of modulator I3a, a modulated wave Een cos Item cos (met), and there is produced at the output of modulator I4, a modulated wave Een sin Icemn sin (nwr'). These two outputs are then added to produce at the output terminals I6. II. a phase-modulated carrier Eon cos (mut-keum), wherein th-e phase angle deviation of the carrier is a linear function of the signal input voltage emu.

Fig. 2 is a schematic diagram of a phase converter adapted to produce the modulating functions defined by Equations 16 and 17, and which may be used to control the generation of the required phase-modulated wave wherein keum is the phase displacement `of the final carrier. This converter consists of a cathode-ray tube I8 having the usual evacuated enclosing envelope I9 provided with the usual electron gun 20 for developing a focussed beam of electrons. This beam is arranged to be deected in substantially perpendicular directions, for example by the usual horizontal beam-deflecting plates 2|, 22, and the usual vertical beam-defiecting plates 23, 24. Mounted adjacent the enlarged end of the envelope 20 is a fiat metal plate anode 25 which is connected to a suitable high voltage terminal 25 on the conventional direct current power supply used with cathode-ray tubes. Mounted in spaced relation to the anode 25 on the side facing the electron gun, is an apertured mask electrode 2'I having a series of specially-shaped apertures 28, 29, 30, etc. While the drawing shows three such apertures, it will be understood that a greater or less number can be used, depending uopn the maximum phase deviation that is required in the phase-modulated carrier.

The radio frequency sweeping oscillator I3 is connected across the vertical plates 23, 24, while the source Il) of the input signals is connected across the horizontal deecting plates 2|, 22. When the input signal voltage emn is Zero, the beam oscillates in a vertical plane along the center line -of the mask as represented by the dot-dash line 3| (Fig. 3) under the influence of the deflecting voltage from the oscillator I3. If in this condition of the beam, the total deflection amplitude in opposite vertical directions with respect to the center of the aperture 29 is equal to the central length of the aperture, the beam will not be intercepted by mask 2'I, and there- 'fore a constant flow of electrons will arrive at the anode 25 throughout each complete cycle of source I3. If the signal emu is slightly increased, for example to move the electron beam to the right or to the left of center, the beam will be intercepted by mask 21 before it has reached its maximum deflection either upwardly or downwardly. The current to anode 25 will therefore be interrupted for an interval before the end of the first quarter of the radio frequency cycle from source I3; the anode current however will be re-established some time after the end of the first-quarter cycle, and then it will again be interrupted before the end of the third-quarter cycle, and again re-established some time after the end of the third-quarter cycle. The average value of the anode current throughout each radio frequency cycle of oscillator I3 will therefore be somewhat less than the anode current under the condition when the beam is oscillating up and down in the horizontal center of the tube.

The anode 25 can be connected to a suitable integrating device or network which may be a filter comprising for example band-pass sections 32a, 32h, coupled by condenser 33 so that the output of the anode circuit is proportional to the average value of the anode current during each radio frequency sweep cycle, while keeping direct current away from the output, as well as keeping away from the output the high frequencies produced by the beam sweeping back and forth under control of the sweep generator. By properly designing the shape or outline of the mask apertures, it is possible to produce an output voltage having a function which is proportional to a large variety of functions of the signal modulating voltage emu. As above pointed out, it is desired to produce an output voltage epn=Gan(t) :Emu COS kemn (19) or epn=Glm(t) :Emn Sin kemn in accordance with Equations 16 and 17.

Considering for the time being Equation 19 only, it is now necessary to determine the shape of the mask which will produce this output function. We first assume that the radio frequency deflecting voltage is sinusoidal in character, the vertical deection, y, being represented by the expression and since from (22) TY Q=f0 1.a (24) where TY is the time when current ceases to iiow. we have y TY inw- 71, L ndt 25) In thi-s case, the anode current Ia is a known and constant quantity, being the normal anode current of the tube when the beam is not intercepted by the mask. The value of average current I is changed by changing the period of time during which the normal anode current flows, and this, in eiect, changes the integration limits. Since Ia is a constant, we can write, for the average current, Ix at a horizontal displacement X It is now evident that, since the configuration of the mask is symmetrical, we need take the average over only one-quarter cycle of the radio frequency deilecting wave, all other quarter cycles being identical. In other words, the time interval over which the integration is carried outis facades@ 17 rhenitheaveragegcurrent isrbysubstitution'in 426) y gg-'1M (-28) It- .is now necessary Lto express .the 'time TY .at Whichlthebeamfis Cut Oiin. terms ofthe lvertical displacement oithe'r beam,in orderto 'determine 'the 'Teqlte lVertical distance Yfrom lthe horicontati.' center vline to the edge o'f .the mask, at y'horizolital displacementX, v.Returning tolEqua'- tion"'2l,.we ndethat 'thetime at which the. beam is displaced a vertical distance-y is (29) il Then the time "IYqat f which :the 'beam i is vdisplaced-.vertically .a distancec'v to the ;edge 'of the :mask'ls l. gli n Substituting' (-30) in (28) we have 2L, X Ix-:r-Vsm 1A (31,)

. It isfseen from :this equationV that if the edge .tof 'thezmask: coincides' with i the maximum beam deilection,l sof-that lL- A; the.' average anode curfrent'is while if Y=0, corresponding to complete extinc- 'tion of the beam :sive crests of the mask configuration. This is.

of course, the equation of a direct current with `a cosine wave =of fthe vsame amplitude superimposed on it. The direct current can be ffiltered later leaving the required cosine function. Then we have, from Equation 31 Simplifying this relationship,v we .obtain lfor 'theequation ofithe'edge ofthe mask The outputcurrent' wave 'given by Equation: 34 is now-passed through a filterto eliminate the direct current. Thealternating current component sets up a voltage wave 'with an amplitude Em across the load impedance,.tc produce .an 'instantaneous'voltagewave estL-'EM cosl` ('37.)

:centimeters vdeiiection @per volt. We then :have

andifweidefine .the constants involvedin accord- -`ance fwith the .equation '2MLl "fik i (40) we obtain :the nal requiredv result,

epnIEmn COS kemn (19) Inra similar manner, it is found that the equa- .tion of rthemask edge-required to produce :the

sine modulating function of Equation 20 is LFig. 4 is Vasgrapli. showing .the outlinesr'ofthe edge .of .the maskrinthe cosine phase converter.

In plotting this curve, Equation y36 has .been

simpliied rbymakng z the following. assumptions;

YI mn=I a ('42) This `assumption results in thel sweeping beam barely reaching .the .edge .of the maskwhen X:0.

YA=1 centimeter (43) 'As-1 centimeter "(44) .The .diameter of the beam at the anode might reasonably .be supposed .tovbe not more than .1 millimeter, and under these conditions it appears that acomplete cycle along thevhorizontal .axis mightoccupy a spaceof notzmore than 1 centimeter; without causing non-linearity. This matter needs to be investigated further experimentally.

Underthese conditions, Equation 36 reducesto whichis the function plotted inl Fig. 4. .Equation 37 also becomes CJmZEmn COS 27X '.(46)

Similarly, the equation'of the edge of'the`-mask in the sine phase converter, making the same assumptions regarding the values lof A `and il, becomesv Y=sin [f1-ru +sin am] '(41) andthe output 'voltage ofthe sine phase converter is BpnlT-Emn Sin 21rX (48) V From Fig. 4. and Equations .46. and 48,. it vis evident that the wavegoes through a complete cycle '(211- radians) of phase deviation as .the beam sweeps to the right or vleft a distance of 1 centimeter. With existing oscilloscopes it is no lproblem `to maintain a linear relation between deecting voltage and beam displacement for displacements from the center line as large as 5 inches or 12.5 centimeters. .It vtherefore seems probable that. with this system. phase deviations as. high :as x25 radians may be achieved.

Instead of using phase converters of .the cathode-ray beam `type to derive the Vsine and cosine modulating functions'according toEquations 16'and17'above-mentioned, a combination of evacuatedy grid-controlled electron tubes can be used. Such an arrangement is schematically illustratedl in Fig. 5. The tubes in each phase converterl are arranged in one'ormoresta'ges, depending -upon the total amount of phase deviation multiplication required in the phasemodulated carrier.

Referring to Fig. which shows a cosine phase converter, the rst stage thereof may comprise a pair of tubes 34, 35, upon whose control grids 36, 31, the input modulating signal emu is impressed. The cathode 38 is returned to the common negative terminal 39 of the direct current power supply through a relatively small cathode load or bias resistor 40; while cathode 4l is returned to the common negative terminal 39 through a relatively large cathode load resistor 42. A common input or grid-leak resistor 43 is provided for both tubes. The anodes or plates 44, 45, are connected to the positive terminal 4B of the direct current power supply through respective equal resistors 41, 48, and also to the cathodes -through respective voltage divider resistors 49, 50, so as to provide the normal flow of biasing current through resistors 49, 42, independent of the plate current of the respective tubes. which are normally at plate current cut-oil?.

When the input signal voltage em is zero, tube 34 is biased just beyond plate current cut-oit by the drop in resistor 40, and tube 35 is biased by resistor 42 a great deal beyond plate current cut-off. As the voltage ema begins to rise, it causes plate current to flow through tube 34, but tube 35 does not pass plate current until tube 34 reaches plate current saturation. The relations of the plate voltages of the two tubes are shown in the respective graphs of Figs. 6 and '7. The combined output of the two tubes is then as indicated by the graph of Fig. 8, and represented by the expression (cos kemn). Any desired number of cycles of phase shift can be produced by adding similar cascaded stages, such as stage #2 wherein the elements are the same as those of the stage #l but with the suix a applied thereto. In other words, the inputs to the two stages are fed in parallel and their outputs are combined in series.

When it is desired to obtain the corresponding sine function (sin kemn), a similar arrangement to that of Fig. 5 may be used, but with higher normal cathode biasing voltages on the tubes to delay the start of the cycle by 90 degrees. The only difference then is that the sine converter uses bias resistors 40, 42, 40a, 42a, of much higher Value than the corresponding resistors 40, 42, 40a, 42a, of Fig. 5.

Fig. 9 shows a modication of Fig. 2, and wherein only one set of beam deflector plates is used. The electron gun 20, instead of developing a cathode-ray beam focussed to a point or spot which is swept vertically along a line, may directly develop a beam in the form of a focussed line 50 which is normally at the center of the aperture 29 (Fig, 9A). The remaining parts of Figs. 9 and 9A are the same as the corresponding parts of Figs. 2 and 3, and are designated alike in both sets of figures. The action of the converter of Fig. 9 is substantially the same as that described above in connection with Fig. 2. The signal voltages impressed on plates 2i, 22, will deilect the line of electrons 50 so as to be variably intercepted by the edges of the aperture 29 in mask 21, to produce at the anode 25 a voltage which is a cosine function of the input signal emn. The sine function of the input voltage emn can then be developed by a similar phase converter, but with the beam being intercepted by a mask having apertures designed in accordance with the above Equations 47 and 48.

Fig. l0 shows another modified form of the phase converter which may be similar to that of Fig. 9, except that the electrodes 25 and 21 are replaced by the mosaic electrode 5I. The remaining parts of Fig. 10 which are identical with those of Fig. 9, bear the same designation numerals. The electrode 5I consists of a series of individual anode targets 52 which are suitably applied or attached in equal spaced relation to a metal backing 53. The targets 52 are of different lengths L, with each target length be ing proportional to a cosine function of the distance D between that target and the center line 54 of the target. One convenient way of accomplishing this result, is to make the plate 53 of thin metal strip which is corrugated or sinuously curved, and to make the individual. targets 52 of the same resistance material. The backing 53 can thenbe connected to the anode supply terminal 26. Consequently the voltage that appears at the output of the system, will depend upon the particular target upon which the cathode-ray beam is impinging, and since the length and resistance of each target vary with its distance from the center line of the anode, the desired sinusoidal function can be obtained. A similar converter can be used to derive the cosine function. In other words, in the sine converter, the lengths of the several targets 52 will correspond in a sinusoidal relation with their respective distances from the center line 54, whereas in the cosine converter the lengths of these targets 52 will vary in length in a cosine relation with respect to their distances from the said center line 54. If desired, both sets of targets may be mounted within the same evacuated envelope I9 and each of course provided with a separate output circuit similar to that illustrated in Fig. 10. In that event, either two separate oscillating cathode-ray beams may be employed, or the same beam may be of suflicient length to simultaneously sweep both sets of mosaic targets. This also applies to the embodiments of Figs. 2 and 9.

While particular embodiments have been described and disclosed herein, it will be understood that .this is done merely for purposes of explanation of .preferredforms of the invention, and that various changes and modifications may be made therein without departing from its spirit and scope.

What is claimed is: y,

l. The method of phase modulation of a carrier under control of a source of variable amplitude signal voltage, which comprises amplitude-modulating a sine function carrier wave by a Voltage having a sine modulating function controlled by said signal voltage to produce a first modulation product, amplitude-modulating a cosine function carrier by another voltage having a cosine modulating function also controlled by said signal voltage to produce another modulation product, and adding said modulation products to produce a phase-modulated output carrier wherein the phase modulations are correlated with said signal voltage.

2. A carrier phase-modulation system, comprising a source of variable amplitude signal voltage, a cosine phase converter, a sine phase converter, means to apply said signal voltage to said converters to produce two separate voltages having modulating functions respectively related by the sine and cosine of an angle corresponding to said signal voltage, a carrier source, means to derive from said carrier source two ll :Separate but aI-doyf cd'prets Which are respectively related byf sine audi cosine func:- tions; a iirst'A amplitude modulator upon which are impressed thecosine functionv offs'aid modulating'" voltage' and the cosine function'-- of saidr carrier to produce a'modulation product "represented bythe productof` the impressed-*func*- tions, a second' 'amplitude modulatorfupon which are impressed* the' sin'e'-v functionv of" saldi modolatihg voltage `andtl're sine Yf unct'ir'm of'sadcan ri'er toproduce anothermodulation product rep'- 'a cathode-ray tube having" an electrongun for dev"slopingv a cathode-raybeam, and a beam: tercjepting: masli electrodeh'avinga series. of similarly shaped apertures; and means 15o-sweep s'iid' lucani` across said apertures in accordance amplitude o rsaid signal vol e Anf arrangement aoco g tol "aim 2^, in

wiiiclieach or said phase converters comprises a cathode-ray tube having electron gun for developing an electron beam, an aperturedbeam iterep'ting mask electrode, and means including said source ofY signal voltage for causing said beam to sweep in mutually coordinate directions 'with respect to the boundary of' the mask apelature'.

o.' An arrangement accordingnto claim 2, in which each of said phase converters comprises a cathode-ray tube having means to develop a beam of electrons which is focussed to a point, an apertured beam intercepting mask' electrode, al local source of sweep Vfrequency for sweeping said beam in one directinr` with respect to said aperture, and' means including saidsignal voltage for sweeping the beam in a transverse direction with respect to said aperture'.

7. An arrangement according' tov claim' 2,. in which each of said phase converters comprises aI cathode-ray tube having means Yto develop a beam of4 electrons which isfocussenv in anarrow une, `an apertur'ed beam intercepting masi: elecfrode, and means to sweep said line transversely with respect to the' aperture in said mask electrede.

8. arrangement according to claim 2, in which each of said phase converters comprises a cathode-ray tube having means to develop a bin of' electrons, an anode uponv which the beai'li'riipiges', means to sweep said beam across one dimension of saidV anode,- said anode having a var-ying' resistance said direction to produce an output voltage Whose' amplitude is determined by the position of the beam on the anode and the 'resistance of the anode at said position.

9. An arrangement for producing a phasemodulated carrier, comprising a source of signal voltage, a pair of phase converters upon which said signal voltage is simultaneously impressed: 'toN product.'A twm separate voltages which are in quadrature.phase;;means to"-y generate two;esmal-frequcncy;v carriers; also of quadrature phase; means to amplitudeemodulate said carriers? respectively' by" said.: modulating voltages, and. meansV to combine. the'.v modulated carriers: to producey an. output' carrierv Whose phase: is-'modulatedtd correspond with: said signalvoltage, arrdzinA which` capisco;y said; phase convertersv comprisesv'a'-l pair of grid-controlled electroni tubes', means: for biassing: the; control? grids of the; tubes to'y differenty levels. so; that one tube does not" becomet'pl'ate' current. conductive until the. other.' tube is atplat'e. currentisaturatloni I0.. arrangement for.'V producing' a' phase'- modulated carrler; comprising' a. source of' signal voltage, ai pair: o f phaseiconverters upon which'. saidv signal' voltage.` is: sinsulta'neousliyl im'- press'ed to produoeltvvo separate'. modulatingvoltages which aresi'n omadraturey phase, means to generate two equal-frequency carriers also of quadrature' phase, meansy to amplitude-modulate said carriers respectively by said modulating'voltages, andi means to combine the modulated carriers-to produceE an output carrier whose phase is modulated to correspond with saidsignal. voltage, and irrvvhich each of 'said phase converters comprises aA pairl or gridi-controlledeleo'- tron'-` tubes, means normally biassing one tube close: to plate, correnti cut-off, means bi'assing the other` tubesubstantiallyA beyond" plate current;v cut=ofi, said otherl tube being' platefconductive only when ther r'stf tube reaches: plate current saturation,- and means to combine the out'- 'puts of' said tubes phase. opposition.

11. An arrangement according to claim 10, and in whichl each phase converter comprises a series ofi similar cascaded stagesv with the number of' stages` determinedfby the total' phase deviation' desiredv in thev phase-modulated carrier.

1'2.The method' of deriving a phase-modulated carrierundercontrol! of'a source of original variable-amplitude signal voltage, which comprises converting thev signal" voltage into twol separate equal-frequency voltages one ofl which is a sine function of the signal voltage and the other a cosine function or" the signal voltage, generating two equal-frequency carriers in respective quadrature phase one of which carriers is a cosinefunction with respect to the other carrier, amplitudemodulating the sine carrier by said sinefunction of the signal voltage, amplitude-modulating' the cosine carrier by said cosine function of the" signal' voltage, and combining the modulated carrl'erstoproduce a phase-modulated output carrier.

DONALD B. HARRIS.

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